Recently, as communication technology and smart device related technology are rapidly developed, a demand for establishing a security system for safely using a communication system and a smart device is also increasing. A basic method of providing security in the communication system and the smart device is to mount a security device implemented not by a memory, but by hardware logic in the communication system and the smart device. According to such methods, a check is performed to determine whether a malignant code exists or an authentication is performed when a security chip is driven and then, software such as an operating system (OS) is driven. Recently, a security technology having the PUF is receiving attention. When the PUF is used, it is possible to prevent an important key, such as an authentication key stored in the security device, from being copied.
A security device can include components to provide digital random signals and a validity detector to detect a validity of the digital random signals and to generate validity signals that represent a detection result. Since a conventional validity detector uses a synchronous configuration, a blind zone is generated every cycle. To be specific, in the conventional configuration, since validity of a digital random signal is detected based on a generated synchronous clock, in a period when the synchronous clock is deactivated, although transition of the digital random signal occurs, it is not possible to detect the transition of the digital random signal.